The invention relates to an arrangement in a thermal device or in a thermal process. The invention also relates to a system comprising a thermal device. Furthermore, the invention relates to the use of an electromagnetic, such as optical, distance measurement instrument for taking measurements of a thermal device. Furthermore, the invention relates to a method for measuring the thickness of a contamination layer on a thermal device. Moreover, the invention relates to a method for cleaning or maintaining, for example sooting, a thermal device. Furthermore, the invention relates to optimizing the cleaning or removing soot of a thermal device.
Thermal devices are used for producing energy or fuel from combustible material. Thermal devices, such as boilers, comprise walls which define, among other things, a furnace and/or flue gas ducts. Moreover, boilers comprise heat exchangers for recovering heat formed in combustion. Both the walls and the heat exchangers comprise surfaces. During combustion of combustible material, flue gases are formed in the furnace. Part of the flue gases contaminate said surfaces. Thus, a layer of soot or ash accumulates on said surfaces. The layer of soot or ash insulates heat and thereby reduces the recovery of heat from the boiler. This is one reason why the surfaces have soot removed every once in a while.
As described above, too infrequent removing soot reduces the recovery of heat from the boiler, because a thick layer of soot or ash can thus accumulate on the heat delivery surface, and the layer insulates heat. Too frequent removing soot, in turn, wears the surfaces of the boiler and the soot removal device itself, reducing their service life. According to the state of the art, the removing soot can be performed, for example, at regular intervals.